To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post LTE system’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like.
In the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
Wireless or mobile (cellular) communications networks in which a mobile terminal (UE, such as a mobile handset) communicates via a radio link to a network of base stations or other wireless access points connected to a telecommunications network, have undergone rapid development through a number of generations. The initial deployment of systems using analogue signalling has been superseded by Second Generation (2G) digital systems such as Global System for Mobile communications (GSM), which typically use a radio access technology known as GSM Enhanced Data rates for GSM Evolution Radio Access Network (GERAN), combined with an improved core network.
Second generation systems have themselves been largely replaced by or augmented by Third Generation (3G) digital systems such as the Universal Mobile Telecommunications System (UMTS), which uses a Universal Terrestrial Radio Access Network (UTRAN) radio access technology and a similar core network to GSM. UMTS is specified in standards produced by 3GPP. Third generation standards provide for a greater throughput of data than is provided by second generation systems. This trend is continued with the move towards Fourth Generation (4G) systems.
3GPP design, specify and standardise technologies for mobile wireless communications networks. Specifically, 3GPP produces a series of Technical Reports (TR) and Technical Specifications (TS) that define 3GPP technologies. The focus of 3GPP is currently the specification of standards beyond 3G, and in particular on standard for the Evolved Packet Core and the enhanced radio access network called “E-UTRAN”. The E-UTRAN uses the LTE radio technology, which offers potentially greater capacity and additional features compared with previous standards. Despite LTE strictly referring only to the air interface, LTE is commonly used to refer to the whole system including EPC and E-UTRAN. LTE is used in this sense in the remainder of this specification, including when referring to LTE enhancements, such as LTE Advanced. LTE is an evolution of UMTS and shares certain high level components and protocols with UMTS. LTE Advanced offers still higher data rates compared to LTE and is defined by 3GPP standards releases from 3GPP Release 10 up to and including 3GPP Release 12. LTE Advanced is considered to be a 4G mobile communication system by the International Telecommunication Union (ITU).
Particular embodiments of the present invention may be implemented within an LTE mobile network (though the present invention may be considered to be applicable to many types of wireless communication network). Therefore, an overview of an LTE network is shown in FIG. 1. The LTE system comprises three high level components: at least one UE 102, the E-UTRAN 104 and the EPC 106. The EPC 106, or core network as it may also be known, communicates with Packet Data Networks (PDNs) and servers 108 in the outside world. FIG. 1 shows the key component parts of the EPC 106. It will be appreciated that FIG. 1 is a simplification and a typical implementation of LTE will include further components. In FIG. 1 interfaces between different parts of the LTE system are shown. The double ended arrow indicates the air interface between the UE 102 and the E-UTRAN 104. For the remaining interfaces user data is represented by solid lines and signalling is represented by dashed lines.
The E-UTRAN 104, or radio access network (RAN) as it may also be known, comprises a single type of component: an eNB (E-UTRAN Node B) which is responsible for handling radio communications between the UE 102 and the EPC 106 across the air interface. An eNB controls UEs 102 in one or more cell. LTE is a cellular system in which the eNBs provide coverage over one or more cells. Typically there is a plurality of eNBs within an LTE system. In general, a UE in LTE communicates with one eNB through one cell at a time, where an eNB may also be referred to as a mobile base station.
Key components of the EPC 106 are shown in FIG. 1. It will be appreciated that in an LTE network there may be more than one of each component according to the number of UEs 102, the geographical area of the network and the volume of data to be transported across the network. Data traffic is passed between each eNB and a corresponding Serving Gateway (S-GW) 110 which routes data between the eNB and a PDN Gateway (P-GW) 112. The P-GW 112 is responsible for connecting a UE to one or more servers or PDNs 108 in the outside world. The Mobility Management Entity (MME) 114 controls the high-level operation of the UE 102 through signalling messages exchanged with the UE 102 through the E-UTRAN 104. Each UE is registered with a single MME. There is no direct signalling pathway between the MME 114 and the UE 102 (communication with the UE 102 being across the air interface via the E-UTRAN 104). Signalling messages between the MME 114 and the UE 102 comprise EPS Session Management (ESM) protocol messages controlling the flow of data from the UE to the outside world and EPS Mobility Management (EMM) protocol messages controlling the rerouting of signalling and data flows when the UE 102 moves between eNBs within the E-UTRAN. The MME 114 exchanges signalling traffic with the S-GW 110 to assist with routing data traffic. The MME 114 also communicates with a Home Subscriber Server (HSS) 116 which stores information about users registered with the network.
In additional to the architectural structure discussed above, LTE also includes the concept of bearers, and in particular, EPS bearers (referred to as bearers for the remaining of this description), where data transmitted from and received by a UE is associated with a particular bearer. Bearers define how UE data is handled as it passes through the LTE network and may be viewed as a virtual data pipe extending through the core network, where a bearer may have quality of service associated with it, such as a guaranteed bitrate for example. A bearer serves to channel packet data to a Packet Data Network (PDN, also referred to as a Public Data Network) outside of the LTE network via the S-GW and P-GW, where a further external non-LTE bearer may be required to channel data from the EPC to an external network. Each bearer is therefore associated with a certain PDN. Each bearer is also identified by a logical channel id (LCID) at the Medium Access Control (MAC) level, where one bearer corresponds to one logical channel.
Within LTE there are two types of EPS bearer: a default bearer and a dedicated bearer. A UE is assigned a default EPS bearer when it first connects to a PDN and it is maintained whilst the UE is still attached to the network, where the default bearer provides a best effort service and thus does not guarantee a particular bitrate. The default bearer also has an associated Internet Protocol (IP) address and a UE may have one or more default bearers.
In addition to a default bearer, a UE may also have one or more dedicated bearers. Dedicated bearers are each associated with a parent default bearer and may provide a particular guaranteed bitrate, which is usually in excess of the bitrate expected of the default bearer. Consequently, dedicated bearers are often used to provide a particular level of service to particular data type, for example, a dedicated bearer may be set up to provide live video to a UE where the dedicated bearer has a relatively high guaranteed bitrate.
A bearer may carry more than one type of data, however, the data packets within each bearer experience the same treatment regardless of their content. Conventionally, data packets sent across a particular bearer each have a Packet Data Convergence Protocol (PDCP) sequence number for re-ordering PDCP PDU's potentially received out of sequence, and also for ciphering/integrity protection. Furthermore, since each bearer may be associated with a particular PDCP reception instance, data packets within LTE are transported with a bearer identification and a packet number such that received data packets can be delivered to the correct PDCP reception instance. For example, the bearer identification may be included in an LTE MAC layer header.
The data packets transmitted over a particular bearer are also associated with a particular IP flow, where a bearer may have a plurality of associated IP flows. The IP flows associated with a bearer relate to a set of data packets that are exchanged between two nodes, for example, a UE and a video streaming server.
An increase in consumer demand for wireless broadband data is evident from the fast uptake of LTE across the world. In view of this, and in view of the relatively high cost associated with increasing the capacity of LTE networks, data service suppliers and operators are increasingly studying how to augment those existing LTE networks. One such method involves using alternative wireless networks to compliment the broadband data services provided via LTE. Here, the operators would be able to offload traffic from the LTE wireless network to an alternative wireless networks, such as WLANs which operate in accordance with the Institute of Electrical and Electronic Engineers (IEEE) 802.11* standards, where this technique of traffic offloading maybe referred to as LTE/WLAN interworking.
In 3GPP Release 12, offloading of data traffic from the LTE RAN (Radio Access Network) is defined for an architecture in which the WLAN is connected to the EPC. This is documented in 3GPP Work Item Description (WID) RP-132101. This offloading comprises the network (specifically the MME) specifying to a UE whether Internet Protocol (IP) traffic transported on bearers related to a PDN are considered to be allowed to be offloaded (offloadable) to a WLAN or not, the final decision on offloading is then performed by the UE. This is defined in TS 24.301 (WLAN offload acceptability 9.9.4.18). In order to enable the UE to determine whether the traffic of bearer is to be offloaded, each LTE cell may broadcast a WLAN cell list and offload thresholds (TS 36.306; section 5.6), relating to for example:
LTE Reference Signal Received Power (RSRP) threshold
LTE Reference Signal Received Quality (RSRQ) threshold
WLAN channel utilisation
WLAN backhaul rate
WLAN Received Signal Strength Indicator (RSSI)
If threshold conditions are met, and the UE has bearers belonging to an “offloadable PDN”, the UE can move traffic from the concerning PDN to WLAN. Note that the network, and in particular the eNB, has no direct control over whether the UE moves traffic since the eNB only provides the thresholds for a decision to be made by the UE.
In order to advance the concept of offloading LTE traffic onto WLANs, 3GPP continues working on two enhancements for the further integration of LTE and WLAN in 3GPP Release 13. These two alternative enhancements may be referred to as 3GPP/WLAN interworking (interworking) and 3GPP/WLAN aggregation (aggregation), where these two approaches differ in the manner in which a WLAN is integrated into the LTE architecture.
FIG. 2 provides a schematic illustration of the architecture for the interworking WLAN-LTE enhancement. The LTE network components correspond to those of FIG. 1, however, a WLAN 200 is integrated with the LTE architecture and is directly connected to the core network (S/P-GW) such that UE mobility between LTE and WLAN is network controlled by, for example, the serving eNB 202 as opposed to the UE as specified in 3GPP Release 12. Data packets may be communicated between the UE and the core network either via the eNB and the conventional LTE air interface or alternatively may be communicated via the WLAN to the core network. The interworking enhancement of FIG. 2 is based on the same architecture as the Release 12 approach to WLAN-LTE offloading described above in which the UE determines which traffic to offload if certain thresholds are met.
In the architecture of FIG. 2, data which would conventionally be communicated via the LTE interface may be offloaded to the WLAN, which among other benefits, may free up resources in the LTE air interface and also potentially provide enhanced data rates to the UE. In this architecture, as opposed to that of Release 12, the mobility of the UE between LTE and the WLAN is network controlled, for example the eNB may issue commands to transfer/offload data traffic from LTE to WLAN. To achieve this, the UE may report a number of measurements to the eNB, such as WLAN RSSI, WLAN cell availability, WLAN backhaul rate, WLAN channel utilisation etc. Based on these measurements, the eNB may then command the UE to move the traffic of certain bearers to the WLAN or back to LTE from the WLAN. It will be appreciated that because traffic sent to/from the core network via WLAN bypasses the eNB, though the eNB may be aware of some WLAN characteristics by virtue of the UE measurement reports, the eNB may not be directly aware of the amount of traffic that is transported over WLAN.
FIG. 3 provides a schematic illustration of the aggregation WLAN-LTE enhancement architecture. The LTE network components correspond to those of FIG. 1, however, a WLAN 200 is integrated into the LTE architecture via a connection to the serving eNB. In this aggregation enhancement, UE mobility between LTE and WLAN is network controlled, by for example, the serving eNB 202. The aggregation enhancement architecture is based on that known for LTE dual connectivity, which will be familiar to the skilled person. Data packets maybe communicated between the UE and the eNB either directly to the eNB via the conventional LTE air interface or alternatively may be communicated via a WLAN to the eNB. Consequently, in contrast to the interworking architecture, the eNB will handle all traffic being transmitted to and received from the UE whether it be via LTE or WLAN. The eNB may setup WLAN cells in addition to LTE cells and parallel traffic streams can occur on both radio interfaces. As for the interworking architecture, data which would conventionally be communicated via the LTE interface may be offloaded to the WLAN, which among other benefits, may free up resources in the LTE air interface and also potentially provide enhanced data rates to the UE.